28 Clarke, TJie Atoviic Theory. 



which reference has already been made. A cluster of 

 smaller particles or corpuscles satisfies the conditions that 

 chemistry imposes on the problem, their ultimate nature 

 being left out of account. For chemical purposes we need 

 not inquire whether the corpuscles are divisible or indivi- 

 sible, although for other lines of investigation this question 

 may be pertinent. But no matter how far we may push our 

 analysis, we must always see that something still lies 

 beyond us, and realise that nature has no assignable 

 boundaries. That which philosophers call " the absolute" 

 or " the unconditioned " is for ever out of our reach. 



Through many theories men have sought to get back 

 a little farther. Among these, Lord Kelvin's theory of 

 vortex atoms is perhaps the most conspicuous, and certainly 

 the best known. It pre-supposes an ideal perfect fluid, 

 continuous, homogeneous, and incompressible ; portions of 

 this in rotation form vortex rings, which, when once set in 

 motion by some creative power, move on indestructively 

 for ever. These rings may be single, or linked or knotted 

 together, and they are the material atoms. The assumed 

 permanence of the atom is thus accounted for, and given 

 at least a mathematical validity, but we have already 

 seen that the chemical units may not be quite so simple. 

 The ultimate corpuscles, to use J. J. Thomson's word, may 

 be vortex rings ; the chemical atom is much more complex. 

 On this theory, chemical union has been explained by sup- 

 posing that vortices are assembled in rotation about one 

 another, forming groups which are permanent under certain 

 conditions, and yet are capable of being broken down. 

 The voriex ring is eternal, its groupings are transitory. 

 This is a plausible and fascinating theory ; if only we can 

 imagine the ideal perfect fluid and apply to it the laws of 

 motion ; that done, all else follows. Unfortunately, how- 

 ever, the fundamental conception is difficult to grasp, and 



